Using a pick and place machine, a component is rotatable with a nozzle (about a rotation axis of the nozzle) in and opposite to a φ-direction, and movable with the nozzle in (i) an XY-plane extending perpendicular to the rotation axis, and (ii) in a Z-direction extending parallel to the rotation axis.
Several methods are known to determine the orientation of a component with respect to a nozzle and/or the pick and place machine. The word “orientation”, used with respect to the component, will be used throughout this document to comprise both the angular position of the component with respect to a nominal φ reference as well as the (x, y) position of the component with respect to a nominal (x, y) reference. Such nominal φ reference may be the reference of rotation axis of the nozzle (e.g., an index position), whilst the nominal (x, y) reference may be the Y-plane extending perpendicular to the rotation axis, centered to the rotation point of the rotational axis. However, other references in the pick and place machine may be used as well.
By a prior art method, sensor data of a sensor is sent to a stationary alignment processing unit. From an actuator for rotating the nozzle, encoder data is also sent to the stationary alignment processing unit. In the alignment processing unit the sensor data and the encoder data are real time combined and are used to compute a correction instruction. The correction instruction from the alignment processing unit is being used to instruct a motion control unit of the actuator. The alignment processing unit and the motion control unit can be located in the same housing or in different housings.
The sensor, the actuator, and the nozzle are typically located in a placement unit, which is movable with respect to the board on which the component is to be placed. The alignment processing unit is located stationary in, or outside, the pick and place machine.
One disadvantage of such a prior art method is that the data from the sensor and the actuator need to be transferred over a relatively large distance to the stationary alignment processing unit, before the sensor data and encoder data are combined. Another disadvantage of such a prior art method is that typically, the sensor read out timing is not synchronised with the rotational speed of the nozzle and one has to operate with constant velocities to minimize jitter between encoder data and sensor data.
To keep data latencies in both communication paths small, including the data transfer in the processing unit, a real time processing environment is desirable.
U.S. Pat. No. 6,195,165 discloses a method whereby the angular position of a component with respect to a nozzle is being sensed and a correction instruction is being computed. The sensing and computing are both carried out in a sensor. The correction instruction is communicated to the pick and place machine and the component is placed on the board as a function of the correction instruction.
By this method, information about the angular position of the nozzle from the actuator, and information from the sensor, are real time combined in the sensor and are used to compute the correction instruction. The computing is being done in a computing part of the sensor.
Such an approach has the advantage in that the distance between the actuator, a sensing part of the sensor and the computing part of the sensor are relatively short. However, typically, the housing of the sensor is small and directly mounted in the placement unit, which also carries the nozzle. Local heat production is to be kept low to prevent heating up of the placement unit. Heat would lead to thermal expansion having a negative effect on placement accuracy. Therefore, power of the processing electronics in the sensor has to be limited. This puts restrictions on the complexity and the speed of calculations to be performed in the sensor. In practice, the rotational speed is typically kept substantially constant, to enable fixed frequency sensor read out and to be able to apply simpler processing routines. Storing of information about the angular position of the nozzle from the actuator and information from the sensor for later analysis is not practical since the memory in the sensor is limited.
Thus, it would be desirable to provide improved pick and place machines, improved sensors for pick and place machines, and improved methods of positioning a component on a board.